Airbags can be used to protect a vehicle occupant during a collision or rollover. Airbags can also be configured to protect specific body components. In this respect, vehicles can be provided with airbags for protecting the occupant""s knee region. Airbags for the knee region (i.e., knee airbags) must absorb relatively high impact energy over a relatively small area within a relatively short displacement. To reliably protect the vehicle occupant""s knee or lower leg, it is necessary for the knee airbag to deploy quickly with a high restraining force.
German patent publication DE 297 10 745 U1 discloses a knee-restraining device having an airbag and a knee catcher plate. The airbag propels the knee catcher toward the occupant""s knee during a collision. Catching straps are needed to fix the end position of the knee catcher plate and to control the path of movement of the knee catcher plate during its deployment. The knee catcher plate advantageously distributes the impact force over a relatively large area so that a higher restraining force can be implemented with a relatively low airbag internal pressure. The knee catcher plate, however, results in a more complicated and costly protection system.
German patent publication DE 298 07 424 U1 also discloses a knee protection device with an airbag configured as a cushion. To apply a high restraining force, the airbag has catching straps that connect opposite portions of the airbag wall, and thus counteract the shape change of the airbag when the knee penetrates it. In addition, the airbag needs partitions that form a plurality of chambers inside the airbag. The catching straps and the airbag partitions likewise involves a more complicated and costly protection system. Moreover, the cushion-shaped airbag creates an unfavorable stress distribution at a relatively high airbag pressure that stresses the seam region. Furthermore, the cushion-shaped airbag blank impairs the restraining action in the edge region due to its decreased depth.
German patent publication DE 295 17 953 U1 also discloses a knee protection device with a cylindrical airbag that is fastened, laced together at its lateral ends to the vehicle. It is therefore not possible to attach the airbag in a vehicle without a lateral fastening means.
Accordingly, there still remains a need to improve an airbag, in particular, for protecting the lower leg portion, including the knee, and a head. The present invention addresses this need.
The present invention relates to an airbag and a method of forming the airbag. The airbag is particularly useful as a head airbag or knee airbag.
The airbag comprises a substantially cylindrical tube folded longitudinally to form a predetermined fold pattern having at least two individual looped segments and a lateral seam that closes each lateral end thereof. The laterals seams maintain the fold pattern. The airbag in the inflated states is substantially cylindrical. The resulting airbag can have relatively short lateral end regions to maximize the cylindrical extent of the inflated airbag. The cylindrical tube can comprise a rectangular fabric layer with a longitudinal seam that joins longitudinal ends thereof.
The predetermined fold pattern includes a half fold, where the cylindrical tube is folded in half longitudinally to form two looped segments. It also includes at least four individually looped segments grouped into two sections having at least two adjacent segments laid one upon another, with the lateral seams maintaining the grouping. In this respect, the airbag can have six looped segments, three to each section. The fold pattern can also include a middle region from the segments can extend outwardly. The middle region can have a clearance.
In another embodiment, the segments overlap one another at least partially in a middle region from which the segments extend outwardly. The overlapping segments can be arranged one above the other in the middle region.
The airbag can further include additional fabric portions inserted at the lateral ends of the airbag between or into the individual segments of the folded airbag, and secured with the lateral seams. The additional fabric portions can be integrally formed with the tube. The additional fabric portions can also comprise double-folded cloth strips pushed from the side between or into the segments before the lateral seams are formed. The additional fabric portions can be inserted into regions of the folded tube having a reduced number of layers arranged one above the other to compensate for varying thicknesses caused by different number of layers.
The longitudinal and lateral seams can be stitches. The region of the fabric layers where the longitudinal seam is formed can have a substantially constant thickness.
The method of forming an airbag comprises providing a substantially cylindrical tube, folding the tube longitudinally to form a fold pattern having at least two individual segments, and closing each lateral end of the tube with a lateral seam, which also maintains the fold pattern.
The tube can be formed by joining together longitudinal ends of a rectangular fabric layer with a seam, such as by folding the rectangular fabric layer in half to align the longitudinal ends.
The folding step can comprise folding the cylindrical tube in half longitudinally to form two individual segments. The folding step can comprise forming at least four individually looped segments and grouping the segments into two sections by situating at least two adjacent segments one next to another. The folding step includes forming six looped segments and grouping the segments three to each section. The folding step can further include forming a middle region from which the segments can extend outwardly, with a clearance. The folding step can include overlapping segments one another at least partially in the middle region from which the segments extend outwardly, with the overlapping segments arranged one above the other in the middle region.
Additional fabric portions can be inserted at the lateral ends of the airbag between or into the individual segments, and secured the fabric portions with the lateral seams.
The other airbag features described above can also be incorporated in the present method.